The present invention relates to a method of driving a display device, a display device and an electronic apparatus and, in particular, to a technique for reducing the power consumption of the display device.
Since passive matrix type liquid-crystal display devices need no costly switching elements and are less expensive than active matrix type liquid-crystal display devices, the passive matrix type liquid-crystal display devices find widespread use as monitors of portable computers and portable electronic apparatuses.
The following methods are known as the methods of driving the passive matrix type liquid-crystal display device.
(1) APT method (IEEE TRANSACTIONS OF ELECTRON DEVICE, VOL, ED-21, No.2, FEBRUARY 1974 P146-155 xe2x80x9cSCANNING LIMITATIONS OF LIQUID-CRYSTAL DISPLAYSxe2x80x9d P. ALT, P. PLESHKO, ALTandPLESHKO TECHNIC).
(2) Smart Addressing (LCD International ""95, Liquid-Crystal Display Seminars held under the sponsorship of Nikkei BP, C-4 Lecture No. (1), by Matsushita of Tottori SANYO Electric, Co., Ltd).
(3) Multi-line driving methods (for example, Japanese Patent Application 4-84007, Japanese Unexamined Patent Publication No. 5-46127, and Japanese Unexamined Patent Publication No. 6-130910).
Besides the demand for miniaturization and light weight, there is a growing demand for longer time of displaying without the need for battery replacement in the field of the portable electronic apparatuses such as cellular telephones and pagers. Therefore, a low power consumption feature is rigorously required of the display device used in such portable electronic apparatuses.
The inventor of this invention has extensively studied the passive matrix type liquid-crystal display device with a view to reducing power consumption.
The study has shown that prior art passive matrix liquid-crystal display devices have to supply an alternating current of 20 V or higher in amplitude to both scanning lines and signal lines even during a display-off time, that the power consumption in the power supply circuit for generating that alternating current is considerably large, and that currents flowing between the scanning lines and the data lines via liquid crystals are also considerably large.
The present invention has been developed with a view to resolving such problems.
One of the primary objects of the present invention is to reduce power consumption of a display device such as a passive matrix type liquid-crystal display device.
In a preferred embodiment of the display device of the present invention, the number of voltage levels of scanning lines during a non-selection period is only one, and to set a display element to a display-off state, the voltage level of the data line corresponding to that display element is set to the voltage level of the scanning lines during a non-selection period.
In such a driving method, if image presentation is performed with the polarity of the selection voltage to the scanning lines being periodically alternated, the voltage level during a non-selection period remains unchanged (at a single level) regardless the polarity of the selection voltage for the scanning lines. By employing the voltage level of the data line as the non-selection voltage level of the scanning line, display-off state is easily performed.
The display-off state means a disabled state of the display. The screen of the display-off state corresponds to the screen in a display-off mode. The display-off mode is a mode available to achieve an extremely low power consumption. In the description that follows, the terms xe2x80x9cdisplay-off statexe2x80x9d, xe2x80x9cdisplay-off modexe2x80x9d, and xe2x80x9cdisplay-off mode screenxe2x80x9d are frequently used.
In the present invention, when a scanning line is set to a non-selection voltage with a data line set to the same voltage, no voltage difference between both lines appears activating a display-off state (display-off mode).
Since the number non-selection voltage levels is only one, the power supply circuit for generating the non-selection voltage is simple, and the power consumption of the power supply circuit is reduced. Compared with the method where the non-selection voltage is changed periodically, equalizing the data line voltage to the scanning line voltage is easy, and the power consumption with a display panel attributed to the voltage difference between the scanning line and the data line is reduced. Thus, power consumption of the display device is accordingly reduced.
Even when a selection pulse enters the scanning line with the voltage level at the data line kept to the non-selection voltage level of the scanning line, the display-off state is maintained. This is because simply selecting a scanning line during a selection-period is not sufficient enough to exceed the threshold of liquid crystal and keeps the display-off state.
Based on this principle, one area in one screen is set to the display-off mode while the remaining area is allowed to present a predetermined image such as icons by controlling properly the voltage applied to the data line.
In a preferred embodiment of the present invention, a display control signal is applied to each of a plurality of ICs to drive the data lines, and by the display control signals, at least parts of data line drive outputs from the ICs are set to the voltage level of the scanning lines during a non-selection period.
A plurality of ICs are arranged as data line drivers, and the data line drive outputs from the ICs on a per IC basis is kept to the voltage level of the scanning lines during the non-selection period. In this way, the area covered by that IC is set to the display-off state (display-off mode).
In a preferred embodiment of the present invention, when at least parts of data line drive outputs are set to the voltage level of the scanning lines during the non-selection period, the supply of, at least, either display data or a high-frequency clock for transferring the display data to the IC is suspended.
By suspending the display data in the area in display-off state (the area in the display-off mode) or the high-frequency clock to be used for the transfer of the display data, low power consumption design-is further promoted.
In a preferred embodiment of the present invention, a display control signal is applied to the driving circuit for the data lines to individually control the data-line drive outputs and to selectively set a desired drive output to the voltage level of the scanning lines during the non-selection period.
With this arrangement, the area in the display-off state is flexibly set.
In a preferred embodiment of the present invention, the data-line driving circuit, constructed of a plurality of blocks, is supplied with the display control signal, which controls the data line drive outputs on a block by block basis so that the data line drive outputs within any block are set to the voltage level during the non-selection period.
In this way, the area in display-off state is flexibly set on a block by block basis.
In a preferred embodiment of the present invention, h scanning lines out of the plurality of scanning lines (h is an integer equal to or greater than 2) are simultaneously selected, and each of the selected scanning lines is supplied with a scan voltage based on a predetermined selection voltage pattern, while each of the data lines is supplied with a voltage that is determined by comparing the selection voltage pattern with the display data representative of the display status of each display element so that a desired display is presented, and to activate no image presentation state (display-off mode screen), the display control signal fed to the data-line driving circuit sets, at least, parts of the data line drive outputs to the voltage level of the scanning lines during the non-selection period.
The driving method of activating the display-off state (display-off mode screen) is applied to a display device which features a known multi-line driving technique.
In this case, along with the advantage of the multi-line driving method that the level of the selection voltage applied to the scanning lines is lowered during image presentation, the effect of low power consumption during the display-off state further promotes reduction of power consumption.
In a preferred embodiment of the present invention, the number of scanning lines, h, simultaneously selected in the multi-line driving is set to be an even number.
When the number of simultaneously selected scanning lines is h, the number of voltage levels of the data lines is necessarily xe2x80x9ch+1xe2x80x9d. If h is an even number, xe2x80x9ch+1xe2x80x9d is an odd number, and the voltage levels of the data lines are symmetrically distributed with its xe2x80x9cpredetermined reference voltage levelxe2x80x9d placed centrally with one half the voltage levels on the positive side and the other half on the negative side of the predetermined reference voltage level. The xe2x80x9cpredetermined reference voltage levelxe2x80x9d can be set to coincide with the scan voltage level during the non-selection period. Specifically, when the number of the simultaneously selected scanning lines is even, the middle one of the voltage levels of the data lines may be set to coincide with the voltage level of the scanning lines during the non-selection period. For this reason, setting a new voltage level for the scanning line during the non-selection period as the voltage level for the data line is not required to activate display-off state. This arrangement simplifies design and avoids an increase in circuit complexity, thereby leading to reduction of power consumption.
In a preferred embodiment of the present invention, the number of simultaneously selected scanning lines is 2, 4, 6, or 8.
As the number of simultaneously selected scanning lines increases, the scale of the circuit for driving them is accordingly enlarged, and the larger-scale driving circuit will work to the contrary to the prime object of the present invention of reducing power consumption. For this reason, the practicable number for simultaneously selected scanning lines, h, is 2, 4, 6, or 8.
The display device of the present invention incorporating the above-described driving method supplies desired data lines with the non-selection voltage, thereby flexibly setting a display-off state area (an area in display-off mode).
In a preferred embodiment of the display device of the present invention, by decoding the display control data and display data, an area to be in display-off state is designated on a per data line basis, or by a combination of a plurality of display control signals, an area to be in display-off state is designated on a per block basis.
In a preferred embodiment of the display device of the present invention, a display-enabled area is set to be smaller in size than the display-off state area (the area in the display-off mode) so that needless power consumption during standby time is restricted.
In a preferred embodiment of the display device of the present invention, the display device has a section that covers at least part of the screen and the area covered by the section becomes a display-off state area.
The area in the display-off state remains invisible to a user. The section that covers at least part of the screen is constituted by at least one movable member, such as a sliding cover. The screen entirely or partly is retracted in the cabinet of the display device depending on operating conditions.
The electronic apparatus of the present invention is the one that incorporates the display device that is capable of designating properly the display-off area.
In a preferred embodiment of the present invention, to drive a display device that comprises N scanning lines (N is an integer equal to or greater than 2), M data lines (M is an integer equal to or greater than 2), a plurality of display elements, the display state of which is controlled by a voltage applied to the scanning lines and a voltage applied to the data lines, a driving circuit for the scanning lines, and a driving circuit for the data lines,
a display control signal is applied to the scanning-line driving circuit, consecutive K scanning lines (K is an integer equal to or greater than 2 but smaller than N) out of the N scanning lines are deselected from the range of selection, based on the display control signal, only (N-K) scanning lines are selected to be displayed, and the scanning line voltage level during the selection period when (N-K) scanning lines are driven is set to be lower than the scanning line voltage level during the selection period when N scanning lines are driven.
When the border of the display-off state area is arranged in the direction of the scanning lines (in the Y direction), K scanning lines corresponding to the display-off state area are excluded from the range of selection. With this arrangement, the duty factor (thus, the number of scanning lines driven) in the driving of the display device changes, and along with the duty factor change, the selection voltage level for the scanning lines for appropriate image presentation is accordingly lowered. The lowered selection voltage level in turn reduces power-consumption.
The change of the voltage level of the scanning lines during the selection period is performed by using the display control signal that changes the level of the voltage a variable voltage source supplies to the scanning-line driving circuit. The variable voltage source may be constituted by a bootstrap circuit, for example.
In a preferred embodiment of the present invention, resolution conversion is performed to a displayed image when the multi-line driving method is employed to present the image.
The resolution conversion is performed by applying the same scan voltage to consecutively arranged Q scanning lines when a resolution 1/Q (Q is an integer equal to or greater than 2) is designated by a resolution conversion signal, and by selecting simultaneously (Qxc3x97h) scanning lines. The resolution 1/Q means not only that the duty factor in the driving of the display device varies, but also that the size of the image is multiplied by Q times. In this case, while power consumption remains almost unchanged, the size of the image is enlarged, and appeal to the user""s vision is substantially increased.
In a preferred embodiment of the present invention, to drive a display device that comprises N scanning lines (N is an integer equal to or greater than 2), M data lines (M is an integer equal to or greater than 2), a plurality of display elements, the display state of which is controlled by a voltage applied to the scanning lines and a voltage applied to the data lines, a driving circuit for the scanning lines, and a driving circuit for the data lines,
the number of voltage levels of the scanning lines during a non-selection period is only one,
a display control signal is applied to the driving circuit for the scanning lines, an area corresponding to consecutive K scanning lines (K is an integer equal to or greater than 2 but smaller than N) out of N scanning lines is set as an area not to be displayed, an area corresponding to the remaining scanning lines is set as a display-enabled area, the K scanning lines are kept to the voltage level during the non-selection period without applying a selection voltage thereto, while the data lines are supplied with the voltage, which is fet for image presentation, for a duration in which the K scanning lines should otherwise be selected.
When the border of the display-off state area is arranged in the direction of the scanning line (in the Y direction), the K scanning lines corresponding to the area in display-off state are included in the range of selection without varying the duty factor in the driving of the device, and on the other hand, the data lines are supplied with the voltage of the level for displaying rather than with the scanning line voltage during the non-selection period, for a duration corresponding to the display-off state area. No change in the selection voltage of the scanning lines is required, because the driving duty factor remains unchanged. Thus, the complexity in the construction of the power supply circuit is not increased. When a driving method of selecting simultaneously a plurality of scanning lines is adopted, the above driving method may be applied.
In a preferred embodiment of the display device of the present invention, during a standby time, the area other than the smallest display area required is set as the display-off state area (screen in the display-off mode) by using one of a variety of above driving methods to reduce power consumption.
In a preferred embodiment of the display device of the present invention, a plurality of switch means are arranged in voltage paths to the scanning lines or data lines, and when no image is presented, the switch means are put to open state to float electrically scanning lines or data lines.
In this case, the conductive paths interconnecting the scanning lines, electro-optic elements such as liquid crystals existing between the scanning lines and data lines, and the data lines are completely disconnected from a voltage source. For this reason, unwanted currents are prevented from flowing through the electro-optic elements. Since the scanning lines and data lines are electrically unstable with this arrangement, an unwanted display may be created by static electricity or the like, and thus a cover is preferably mounted entirely on a display panel to relieve the user of uncomfortable feelings.
In a preferred embodiment of the display device of the present invention, at least two display panels are provided, and the duty factor in the driving of one of the two panels is adequately set so that the selection voltage level of the scanning lines are set to coincide with the voltage level applied to the data lines. With this arrangement, the construction of the power supply circuit is simplified.
In a preferred embodiment of the display device of the present invention, the driving circuit for driving a display matrix is provided with both one function for driving the scanning lines and the other function for driving the data lines.
The functions of the driving circuit are adequately switched in accordance with the size and shape of image display area to vary the duty factor in the driving of the device, and thus the voltage of the scanning lines during selection period is reduced, and thus the power consumption during image presentation is reduced.
FIG. 1A shows exemplary voltage levels of scanning lines and data lines in the driving method of the display device of the present invention, FIG. 1B shows another exemplary voltage levels for the scanning lines and data lines,
FIG. 2 shows the principle of the driving method of the display device of-the present invention,
FIG. 3A shows an exemplary construction of the passive matrix type liquid-crystal display device which incorporates the driving method of the present invention, FIG. 3B shows an exemplary display screen of the device of FIG. 3A,
FIG. 4A shows another exemplary construction of the passive matrix type liquid-crystal display device which incorporates the driving method of the present invention, FIG. 4B shows an exemplary display screen of the device of FIG. 4A,
FIG. 5 shows voltage levels for the scanning lines and data lines in the present invention where the driving method of sequentially selecting the scanning lines one by one (ATP driving method) is incorporated,
FIG. 6 shows the relationship between applied voltage and light transmittance ratio in the liquid-crystal display device,
FIG. 7A shows an exemplary construction of the passive matrix type liquid-crystal display device which incorporates the driving method of the present invention, FIG. 7B is a timing diagram showing the operation characteristic of the device of FIG. 7A,
FIG. 8A is a timing diagram showing an exemplary operation of the liquid-crystal display device of FIG. 7A, FIG. 8B is a timing diagram showing another exemplary operation,
FIG. 9 shows an exemplary construction of the passive matrix type liquid-crystal display device which incorporates the driving method of the present invention,
FIG. 10A is a timing diagram showing an exemplary operation of the liquid-crystal display device of FIG. 9, FIG. 10B is a timing diagram showing another exemplary operation,
FIG. 11 shows an exemplary construction of the liquid-crystal display device of the present invention,
FIG. 12A, FIG. 12B, and FIG. 12C respectively show display controls in the liquid-crystal display device of FIG. 11,
FIG. 13 is a block diagram showing an exemplary construction of a major portion of the liquid-crystal display device of the present invention,
FIG. 14 is a block diagram showing another exemplary construction of the major portion of the liquid-crystal display device of the present invention,
FIG. 15 shows a specific circuit arrangement of the decoder of FIG. 14,
FIG. 16A shows voltage levels for the scanning lines and data lines when four scanning lines are simultaneously selected to be driven, FIG. 16B shows the relationship between the number of simultaneous selection and the number of voltage levels for the data lines,
FIG. 17 is a block diagram showing an exemplary construction of the liquid-crystal display device of the present invention into which a multi-line driving method is implemented,
FIG. 18 is a block diagram showing another exemplary construction of the liquid-crystal display device of the present invention into which the multi-line driving method is implemented,
FIG. 19 shows an exemplary construction of the major portion of the liquid-crystal display device in FIG. 17 or FIG. 18,
FIG. 20 is a diagram showing the feature of the multi-line driving method,
FIG. 21 is a diagram showing the feature of the operation of the multi-line driving method,
FIG. 22 shows the changes of voltages for the scanning lines, data line and pixels in the liquid-crystal display device which incorporates the multi-line driving method,
FIG. 23A and FIG. 23B respectively show exemplary scan voltage patterns in the multi-line driving method,
FIG. 24A shows an exemplary construction of the liquid-crystal display device of the present invention (in which display control is performed in the direction in which the scanning lines are arranged), FIG. 24B shows the display control in the liquid-crystal display device of FIG. 24A,
FIG. 25 shows an example of display control in the liquid-crystal display device of the present invention,
FIG. 26 shows an example of a variable voltage source (a bootstrap circuits shown in FIG. 25,
FIG. 27 shows an exemplary construction of the liquid-crystal display device that incorporates the multi-line driving method to carry out the display control shown in FIG. 25,
FIG. 28A shows a screen on which no image is presented, FIG. 28B shows a screen, one half of which presents an image, FIG. 28C shows a screen, which presents the image of FIG. 28B in double sizing (with a resolution of half that of the image of FIG. 28B),
FIG. 29 is a schematic diagram of a circuit for performing resolution conversion as shown in FIG. 28B and FIG. 28C,
FIG. 30A and FIG. 30B respectively show the operation of the circuit shown in FIG. 29,
FIG. 31 shows specifically display control carried out by the liquid-crystal display device (incorporating the multi-line driving) of the present invention,
FIG. 32 is a timing diagram showing the operation of the device of FIG. 31,
FIG. 33 is a block diagram showing an exemplary construction of the liquid-crystal display device that carries out the display control shown in FIG. 31,
FIG. 34A shows a major portion of the construction of the liquid-crystal display device of the present invention, FIG. 34B shows the feature of the construction of FIG. 34A,
FIG. 35 shows-a major portion of the construction of the liquid-crystal display device which incorporates the multi-line driving method and carries out the display control shown in FIG. 34A and FIG. 34B,
FIG. 36 is a schematic diagram showing a more specific construction of the construction shown in FIG. 35,
FIG. 37 is a diagram showing an exemplary construction of the liquid-crystal display device of the present invention,
FIG. 38 is a diagram showing an exemplary construction of the liquid-crystal display device of the present invention,
FIG. 39A is a front view showing a portable telephone in its normal use which incorporates the display device of the present invention, FIG. 39B is a front view showing the portable telephone of FIG. 39A in its special use,
FIG. 40A and FIG. 40B are respectively perspective views showing a portable electronic dictionary,
FIG. 41A and FIG. 41B are respectively external views of an electronic apparatus which incorporates the display device of the present invention,
FIG. 42A and FIG. 42B are respectively perspective views showing a portable electronic translator,
FIG. 43 is an external view of a portable telephone which incorporates the display device,
FIG. 44 is a diagram showing a major construction of a standard passive matrix type liquid-crystal display device,
FIG. 45 is a diagram showing voltage levels for scanning lines and data lines in the driving method of a prior art liquid-crystal display device,
FIG. 46 is a timing diagram showing the operation of a standard passive matrix type liquid-crystal display device, and
FIG. 47 is a diagram showing the problem associated with the driving method of the prior art liquid-crystal display device.